Dragonfly http://www.dragonflybsd.org/Main/ is also another bsd (a recent fork of freebsd 4.X with some interesting goals) Free has the largest following and is quite good for a desktop as well as server. Net is very oldschool and more true to the original nixes, the people who use it tend to love it and swear by it. Open is a quick and easy server as it is locked down prettty good so you don't need to do a lot to secure it (its more work to make it in to a desktop).